Effects of feeding behavior of rats of a cryptic peptide from the C-terminal end on prepro-growth hormone-releasing factor

A novel cryptic peptide derived from the rat neuropeptide FF precursor reverses antinociception and conditioned place preference induced by morphine

Neuropeptide FF (NPFF) precursors from different species contain at least three known neuropeptides, i.e. FF (FLFQPQRF-NH(2)), AF (AGEGLSSPFWSLAAPQR-NH(2)) and SF (SLAAPQRF-NH(2)). We demonstrate that the rat NPFF precursor contains another bioactive sequence, NAWGPWSKEQLSPQA, spanning between positions 85 and 99. Synthetic NPFF precursor (85-99) (10 and 20 nmol, i.c.v.) blocked the expression of conditioned place preference induced by morphine (5 mg/kg, s.c.). This peptide alone (10 and 20 nmol, i.c.v.) had no influence on the baseline latency of a nociceptive reaction but reversed the antinociceptive activity of morphine (5 mg/kg, s.c.) in the tail-immersion test in rats. These data suggest the existence of a novel bioactive cryptic peptide within an already known NPFF precursor.

Identification of the endogenous ligands for chicken growth hormone-releasing hormone (GHRH) receptor: evidence for a separate gene encoding GHRH in submammalian vertebrates

It is generally believed that hypothalamic GHRH activates GHRH receptor (GHRHR) to stimulate GH synthesis and release in the pituitary of mammals. However, the identity of the endogenous ligand of GHRHR is still unresolved in submammalian vertebrates including birds. In this study, we have successfully identified the chicken GHRH (cGHRH) gene, which consists of seven exons including two exons (exons 4 and 5) coding for the predicted mature GHRH peptide of 47 amino acids. Interestingly, the differential usage of splice donor sites at exon 6 results in the generation of two prepro-GHRHs (172 and 188 amino acids in length) with different C-terminal tails. Similar to mammals, cGHRH was detected to be predominantly expressed in the hypothalamus by RT-PCR assay. Using the pGL3-CRE-luciferase reporter system, we further demonstrated that both the synthetic cGHRH peptides (cGHRH(1-47) and cGHRH(1-31)) and conditioned medium from CHO cells expressing cGHRH could strongly induce luciferase activity via activation of cGHRHR, indicating that cGHRH could bind cGHRHR and activate downstream cAMP-protein kinase A signaling pathway. Using the same system, cGHRH-like peptide was also shown to be capable of activating cGHRHR in vitro. As in chicken, a conserved GHRH gene was identified in the genomes of lower vertebrate species including zebrafish, fugu, tetraodon, and Xenopus by synteny analysis. Collectively, our data suggest that GHRH, perhaps together with GHRH-like peptide (chicken/carp-like), may function as the authentic endogenous ligands of GHRHR in chicken as well as in other lower vertebrate species.

Perimenopausal obesity

In recent years perimenopausal obesity has attracted much attention, because it affects as many as 60% of women of menopausal age. The severe clinical implications of obesity directed our efforts to establish etiological factors and possible ways of treatment. It is clear that there are numerous conditions that underly perimenopausal obesity. Among these, genetic factors, neuropeptides, adrenergic nervous system activity and hormones play a role. Reproductive hormones are also an important factor, but their influence on adipose tissue is only indirect because there are no receptors for sex steroids in fatty tissue. Reports of hormone replacement therapy in women of postmenopausal age have come to different conclusions, so its influence on the etiology of perimenopausal obesity cannot be completely excluded. However, the potential benefit of this kind of treatment in female patients at menopausal age must always be considered.

The nutrient balance hypothesis: peptides, sympathetic activity, and food intake

Food intake can be increased or decreased after either central or peripheral administration of peptides. Galanin, neuropeptide Y, opioid peptides, growth hormone releasing hormone and desacetyl-MSH increase food intake whereas insulin, glucagon, cholecystokinin, anorectin, corticotropin releasing hormone, neurotensin, bombesin, enterostatin, cyclo-his-pro and thyrotropin-releasing hormone reduce food intake. A number of these peptides also affect the activity of the sympathetic nervous system. The peptides which have been tested have a reciprocal effect on food intake and sympathetic activity. Opioids, NPY and GHRH, which increase food intake, decrease sympathetic activity. Conversely, peptides which reduce food intake, increase sympathetic activity, with glucagon, cholecystokinin, corticotropin releasing hormone, calcitonin, neurotensin and bombesin being examples, Several of these peptides also affect the intake of specific nutrients. Insulin reduces food intake in animals fed a high carbohydrate diet, but not when fed a high fat diet. Neuropeptide Y increases carbohydrate intake. Galanin and opioid peptides increase fat intake. Enterostatin and cyclo-His-Pro, on the other hand reduce fat intake. Glucagon decreases protein intake. The effect of peptides on the intake of specific nutrients suggests that peptides may work in part by modulating basic feeding mechanisms to lead to the selection of specific nutrients from the diet. This hypothesis might be called a nutrient specific model of peptide-induced food intake.

Food intake, sympathetic activity, and adrenal steroids

Food Intake is reciprocally related to the activity of sympathetic nerves to brown adipose tissue. This reciprocal or feedback relation is shown for hypothalamic lesions, drugs, and many peptides. These peptides also modulate intake of specific nutrients. Galanin and opioids increase fat intake, whereas enterostatin decreases fat intake. NPY increases carbohydrate intake and growth hormone releasing hormone decreases protein intake. The activity of the sympathetic nervous system is low in obesity and adrenalectomy reverses this decrease in sympathetic activity and reverses or stops the progression of obesity. One mechanism for this effect of adrenal steroids is through a transacting substance which is involved in steroid actions and the production of obesity.

Enterostatin suppresses food intake following injection into the third ventricle of rats

The effect on food intake of an activation peptide from pancreatic pro-colipase, called enterostatin, has been studied after parenteral or third ventricular administration. The activation peptide (enterostatin = Val-Pro-Asp-Pro-Arg = VPDPR) reduced food intake when given intraperitoneally. Low doses of this peptide also reduced food intake when given into the third ventricle, but high doses were ineffective. Enterostatin did not modify the stimulatory effects on food intake of clonidine, an alpha 2-adrenergic agonist, suggesting that its anorectic effects are not mediated via the alpha 2-adrenergic system. These data suggest that enterostatin, an activation peptide from pro-colipase, may play a role in producing satiety.

Acetylation alters the feeding response to MSH and beta-endorphin

The effects on food intake of the N-acetylation of MSH and beta-endorphin have been examined following their injection into the third ventricle. Desacetyl-MSH and alpha-MSH were injected into fasted rats, and beta-endorphin and N-acetyl-beta-endorphin into fed rats. Desacetyl-MSH had no effect on food intake following ICV injection into food-deprived rats at any dose between 100 and 2500 pmoles. Alpha-MSH, the N-acetylated form of MSH, on the other hand, showed a highly significant inhibition of food intake in food-deprived rats with doses of 100 and 250 pmoles but no effect with the higher doses. With beta-endorphin, there was a dose-related biphasic effect. One hour after injection of beta-endorphin (2500 pmole) food intake was inhibited whereas the lowest dose, 100 pmole, significantly stimulated it. By 3 hours, the 2 lowest doses of beta-endorphin both significantly stimulated food intake, but the highest dose remained inhibitory. By 6 hours all doses of beta-endorphin stimulated food intake compared to the vehicle-treated animals. In contrast, N-acetylation of beta-endorphin eliminated all effects on food intake following injection into the third ventricle. These data suggest that N-acetylation of products formed by the processing of POMC can markedly alter their biological properties.

Effects of neuropeptide Y on norepinephrine and serotonin metabolism in rat hypothalamus in vivo

A double-barrelled cannula and microdialysis system were used to inject 100 pmoles of neuropeptide Y (NPY) and to collect from the local microenvironment samples of norepinephrine, 3-methoxy-4-hydroxyphenylglycol (MHPG), serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC) a metabolite of dopamine. Following the administration of 100 pmoles of NPY into the ventromedial hypothalamus of conscious rats, there was a significant reduction in the local concentration of norepinephrine and an even greater reduction in the concentration of its metabolite, MHPG, as compared to saline-injected controls. The concentration of serotonin and its metabolite 5-HIAA as well as DOPAC were also reduced in the ventromedial hypothalamus following local injection of NPY. When NPY was injected into the lateral hypothalamus and monoamines measured from areas adjacent to the injection of NPY there was a significant increase in norepinephrine release and a significant increase in the concentration of DOPAC. Serotonin was significantly decreased and there was an increase in the ratio of 5-HIAA to serotonin. NPY is known to stimulate food intake when injected into either area. The present data are consistent with the concept that a reduction in concentration of serotonin is involved in the regulation of food intake following injection of NPY.

Nutrient balance and obesity: an approach to control of food intake in humans

This article has examined the regulated systems that control nutrient balance. From this analysis, the following conclusions may be suggested: 1. Each nutrient is regulated separately in a feedback system. 2. The control of glucose is regulated by the size of the glycogen stores; the size of the fat depots, by the rate of hepatic fatty acid oxidation; and protein, by the size of the protein depots. 3. Obesity can occur as a result of hyperphagia or from repartitioning the deposition of nutrients. In either case, there is a relative or absolute reduction in the activity of the sympathetic nervous system, requiring adequate levels of circulating corticosteroids.

Attenuation of anorexia induced by heat or surgery during sustained administration of ginsenoside Rg1 into rat third ventricle

Effects of ginsenoside Rg1 (Rg1), a major component of panax ginseng, on modulation of ingestive behavior were investigated. No direct effect was observed on food intake after 10 microliters infusion of 1.0, 2.0, 4.0 or 8.0 mM Rg1 into the rat third ventricle for 10 min. Continuous osmotic infusion of 4.0 mM Rg1 at a rate of 0.966 microliter/h into the third ventricle prevented feeding suppression caused by surgical procedure to implant an osmotic minipump. Continuous infusion of Rg1 attenuated anorexia, increased water intake, and decreased ambulation, that were produced by elevation of environmental temperature from 21 degrees C to 30 degrees C. Consequently, rats maintained body weight and rectal temperature unchanged. The results indicate that sustained central administration of Rg1 may relieve anorexia caused by implantation surgery or by a heated environment.

Experimental obesity: a homeostatic failure due to defective nutrient stimulation of the sympathetic nervous system

The basic hypothesis of this review is that studies on models of experimental obesity can provide insight into the control systems regulating body nutrient stores in humans. In this homeostatic or feedback approach to analysis of the nutrient control system, we have examined the afferent feedback signals, the central controller, and the efferent control elements regulating the controlled system of nutrient intake, storage, and oxidation. The mechanisms involved in the beginning and ending of single meals must clearly be related to the long-term changes in fat stores, although this relationship is far from clear. Changes in total nutrient storage in adipose tissue can arise as a consequence of changes in the quantity of nutrients ingested in one form or another or a decrease in the utilization of the ingested nutrients. A change in energy intake can be effected by increased size of individual meals, increased number of meals in a 24-hour period, or a combination of these events. Similarly, a decrease in utilization of these nutrients can develop through changes in resting metabolic energy expenditure which are associated with one of more of the biological cycles such as protein metabolism, triglyceride for glycogen synthesis and breakdown, or maintenance of ionic gradients for Na+ + K+ across cell walls. In addition, differences in energy expenditure related to the thermogenesis of eating or to the level of physical activity may account for differences in nutrient utilization.

Neuropeptide K suppresses feeding in the rat

We studied the effects of neuropeptide K (NPK), a 36 amino acid residue peptide of the tachykinin family, on latency to onset of feeding and cumulative 1 and 2 h food intake in three experimental paradigms. Intraperitoneal injection of NPK (1.25 and 3.14 nmol) to food-deprived rats delayed the onset of feeding and significantly decreased the cumulative food intake. Intraperitoneal injection of NPK (1.25 and 3.14 nmol) to water-deprived rats produced no effect on subsequent drinking behavior. Similarly, intraperitoneal injection of NPK (3.14 nmol) 15 min before onset of the dark phase (of the light-dark cycle) significantly delayed the occurrence of ingestive behavior and the cumulative food intake was markedly suppressed. Furthermore, administration of NPK intraperitoneally (0.5-3.14 nmol) 15 min before intraventricular (i.c.v.) injection of neuropeptide Y (NPY 0.47 nmol) to satiated rats significantly suppressed NPY-induced feeding and delayed the onset of ingestive behavior. However, when administered centrally prior to NPY injection, NPK delayed the onset of feeding response only. Collectively, these findings show that NPK can acutely and consistently suppress feeding behavior.